The Perpetual Harvest Greenhouse System provides an indoor ecosystem capable of growing equal yields of organic produce 52 weeks per year. This system creates 365 ideal growing days per year by optimizing light, carbon dioxide enrichment, and soluble nutrients in conjunction with continuous planting and harvesting. Because the geo-hydroponics (organic) based Perpetual Harvest system can economically simulate warm season growing conditions, crops that would otherwise be shipped from warmer climates can be grown profitably in colder climates during winter months.
Such
off-season production significantly increases return on investment of the
Perpetual Harvest system in comparison to conventional greenhouse systems
because heating and cooling costs could be up to 75% less than for the standard
three-season greenhouse operation. This system also allows a greenhouse
operator to create growing conditions unique to specific crops such that almost
any crop can be harvested at any time of year, even in colder climates.
The
Perpetual Harvest Greenhouse system accomplishes profitable year round
production by optimizing two primary features of greenhouse operation – Growing
techniques and Energy management. This system
integrates the latest innovations in greenhouse design and operation with
emerging understanding of growing techniques to create production levels not
possible in an outdoor system, or in a three-season greenhouse. Because
this system can operate for four seasons, its yearly energy usage exceeds that
of the three-season greenhouse, however its overall profitability is 6-8 times
that of the conventional three-season greenhouse or outdoor plantings because
the system can provide organic produce when other systems can not. The
uniqueness of the Perpetual Harvest system lies not in any one feature, but
instead in the integration of many innovative aspects of greenhouse design and
operation.
All the
features utilized in the Perpetual Harvest system have been successfully
applied in existing growing systems; however, research indicates that no single
publicized greenhouse system currently in operation utilizes the combination of
features integrated into the Perpetual Harvest system. Furthermore, the
Perpetual Harvest system can be easily integrated with renewable energy systems
such as a bio-diesel plant, ethanol still, methane bio-digester, and/or
co-generation unit, thus improving energy efficiency, driving down operating
costs, and producing marketable fuel by-products.
Optimizing
Growing Conditions
The
Perpetual Harvest system utilizes unique growing techniques to maximize plant
growth. Enhanced growing techniques include: providing artificial light, carbon
dioxide (CO2) enrichment, and maximizing soluble nutrients absorbed through
roots and leaves. The system enhances growth by proportionally increasing the
five most important growing conditions at certain times of the day, thus
producing a ‘supercharged’ growing environment causing plants to reach erectly
for the light while rapidly absorbing nutrients. The result is a significant
and rapid growth surge. Plants can process approximately twice as many
nutrients if light, CO2, and soluble nutrients are increased in balance at the
same time. Standard greenhouse growing temperature is ~85°F, while experience
indicates temperature can be successfully increased to 95°F with increased
light, CO2, and soluble nutrient levels, along with additional water. Growing
at increased temperature has the added advantage of allowing the greenhouse to
remain sealed longer from the outdoor atmosphere each day, leaving the higher
CO2 concentration available for a longer period. With normal light, CO2, and
soluble nutrient levels, plants become stressed at temperatures above 85°F –
not so, with the Perpetual Harvest system. Operating at higher greenhouse
temperatures effectively utilizes periods where it is difficult to maintain
greenhouse temperatures less than 85°F.
Light:
In the
Perpetual Harvest system, plants receive the same amount of light from the fall
equinox until spring equinox by adjusting day length with artificial sunlight.
Experience indicates that ~11 ½ hours is optimal daylight length for most
common food plants in temperate zones . Additionally, applying supplemental
light for three hours each morning, every day of the year, at the same time
that the CO2 concentration is enriched, has been seen to maximize plant growth.
Increased light supports CO2 absorption by stimulating plants to open
their stomata. Supplementing the red, blue, and yellow light frequencies during
this enhanced growth period optimizes utilization of the added light. Red
and blue frequencies (from halide lamps) enhance vegetative growth while yellow
frequencies (from high-pressure sodium bulbs) enhance fruit set and
development.
Carbon
Dioxide Enrichment:
Normal
atmospheric CO2 concentration is ~370 ppm, however, experience indicates that
some plants prefer up to 2000 ppm CO2 (approximately five times normal). In the
Perpetual Harvest system this increased level is maintained for only 3 hours in
the mid morning. During this 3 hour period, the plants store CO2 that will be
used to boost plant growth later in the day after CO2 level has returned to
normal. CO2 is primarily produced by a flame (propane or natural gas) CO2
generator. The flame can serve as a ‘peaking CO2 generator’ and baseline CO2
levels could be provided by decomposing compost or other continuous low
producing sources. A digital CO2 monitor determines when CO2 generators will
cycle, and also serves as an alarm for humans to take precaution when in the
greenhouse during the high CO2 period .
Soluble
Nutrients:
The
Perpetual Harvest system utilizes the ebb and flow style of geo-hydroponics,
passing organic nutrients through a soil-less growing medium placed in plastic
lined beds. Pearlite, pumice, vermiculite, and decomposing organic matter
(potting soil) comprise the soil-less growing medium. Using a soil-less growing
medium greatly reduces the likelihood of soil borne diseases and pests that can
proliferate in the enclosed greenhouse space. Soluble nutrients are provided by
addition of organic compost tea created using the traditional Indore compost
method developed by Sir Albert Howard . This method, based on years of compost
experimentation, produces compost from decomposing cellulose products such as
peat moss, straw, and last season’s crop residue mixed with already composted
animal manure along with a small amount of real soil and recently finished
compost as an inoculant.
In the
Perpetual Harvest system, Indore compost is made using only organic ingredients
mixed in a 25:1 ratio of carbon to nitrogen. Earthworms are added to the pile
after the initial heating period (~8 days) to convert the existing nutrients
into worm castings, a nutrient form more easily accessible to plants. After 14
days, compost is old enough to use as a nutrient base for making compost tea
and/or growing medium. Foliar feeding of this compost tea, applied to the
underside of leaves, is also performed in conjunction with the three-hour
mid-morning light/CO2 enrichment period. After worm digestion, the compost can
be mixed with last season’s used growing medium at a mixture rate determined by
muscle testing . During this enhanced mode of operation, daily muscle testing
(kinesiology) is utilized to provide the data needed to fine-tune light,
nutrient, and temperature levels.
Energy
Management System
Energy
costs are the most expensive aspect of greenhouse operation. The Perpetual
Harvest system capitalizes on recent innovations in greenhouse design to
significantly reduce energy inputs. This reduction is primarily achieved
through two aspects – Insulation design and Energy storage and transfer. Other
aspects, such as greenhouse layout and temperature control also enhance
efficiency, but to a lesser extent.
Insulation
Design:
The south
facing wall of the Perpetual Harvest greenhouse is composed of double layers of
polyethylene, between which are injected biodegradable soap bubbles. The soap
bubbles are fed into a distribution plenum at the top of the greenhouse where
they emerge at intervals along the length of the greenhouse, and flow down to
fill the space between the polyethylene sheets.
